Many oil reservoirs have been discovered which contain vast quantities of oil but little or no oil has been recovered from many of them because the oil present in the reservoir is so viscous that it is essentially immobile at reservoir conditions and little or no petroleum flow will occur into a well drilled into the formation even if a natural or artificially induced pressure difrerential exists between the formatio and the well. Some form of supplemental oil recovery must be applied to these formations which decreases the viscosity of theoil sufficiently so that it will flow or that can be dispersed through the formation to a production well and therefrom to the surface of the earth. Thermal recovery techniques are quite suitable for viscous oil recovery and steam flooding is the most sucessful thermal oil recovery technique yet employed commercially.
Steam may be utilized for thermal stimulation for viscous oil production by means of a steam drive or steam throughput process in which steam is injected into the formation on a more or less continuous basis by means of an injection well and oil is recovered from the formation from a spaced-apart production well. One of the problems often associated with steam flooding is that sweep efficiency can be low unless very small flood patterns are used. This can occur because vertical fractures or other perferred pathways for flow channels are developed during the flooding process with the result that the steam or hot condensed water travels rapidly through the preferred flow channels causing water oil ratios and heat losses too high for economic production. The problem is caused by the vertical shape of the preferred path which limits the area available for heat transfer fromthe steam or hot water to the oil. In this invention an operating procedure is described which forces the preferred flow channel or pathway of the injected steam to be horizontal and to consequently have a much larger area available for heat transfer from steam or hot water to oil. The added efficiency in heating the oil permits greatly increased oil recovery.